1. Field of the Invention
This invention relates to a voltage control oscillation circuit and an adjusting method for the same, in particular, to a voltage control oscillation circuit and an adjusting method for the same, which enables an adjustment for suppressing the dispersion of output characteristics of the oscillation circuit, in spite of the manufacture-related dispersion of the characteristics of circuit elements, when the circuit is incorporated into an IC.
2. Description of Related Art
A demand for fewer components in various electronic devices, typically in mobile radio communication devices including cellular phones, has been increasing in recent years. For example, an oscillation circuit built in an IC in a mobile radio communication device is expected to reduce the number of components used in the device. As an instance of such an oscillation circuit, a voltage control oscillation circuit (hereinafter referred to as VCO circuit) is shown in FIG. 12. The VCO circuit in FIG. 12 includes a resonance circuit consisting of an inductor section 101 and a capacitance section 102. The oscillation frequency f of the resonance circuit is given by the following equation (10):f=1/(2π×(L×C)1/2)where L is the inductance of the inductor section 101 and C is the capacity of the capacitance section 102.
The capacity of variable-capacitance diodes in the capacitance sections 102 is changed by an incoming control voltage VT, which means the control voltage VT adjusts the oscillation frequency f. The VCO circuit arranged like this constitutes a phase lock loop (hereinafter referred to as PLL). The oscillation frequency f of the VCO circuit is conformed to a preset frequency of the PLL for a practical application.
A method for correcting the dispersion of circuit elements and adjusting a variable range of the oscillation frequency of output from a VCO circuit in a frequency synthesizer is disclosed in Japanese Unexamined Patent Publication No. 2000-332606. As shown in FIG. 13, an output signal from a VCO (voltage control oscillator) 110 is divided and divided signals are subjected to phase comparison with a reference signal from a reference oscillator 162 at a phase comparator 163. Compared signals are sent to a LPF (low-pass filter) 150, where the signals are converted into DC voltage signals, which are then applied to a variable resonance circuit, which includes variable-capacitance diodes, in the VCO 110. Meanwhile, an adjusting circuit 170 compares an inner reference voltage with an output control voltage from the LPF 150, and adjusts the resonance circuit in the VCO 110 so that an output frequency of the VCO 110 becomes within a desired variable range.
A technique related to the above method is also disclosed in Japanese Unexamined Patent Publication No. H10(1998)-256904.